Inventions: TelescopesA telescope is a device that lets us view distant objects. Early telescopes (and most today) used glass lenses and/or mirrors to detect visible light. Some modern telescopes gather images from different parts of the electromagnetic spectrum, from radio waves to gamma rays. Most telescopes are located on Earth, but others are in space.

Refracting TelescopesThe first refracting telescope was invented by Hans Lippershey in 1608. Lippershey (1570?-1619) was a German-born Dutch lens maker who demonstrated the first refracting telescope in 1608, made from two lenses; he applied for a patent for this optical refracting telescope (using 2 lenses) in 1608, intending it for use as a military device.

In 1609, Galileo was the first person to use a telescope to observe the skies (after hearing about Hans Lippershey’s newly-invented telescope). Galileo discovered the rings of Saturn (1610), was the first person to see the four major moons of Jupiter (1610), observed the phases of Venus, studied sunspots, and discovered many other important phenomena.

Isaac Newton improved the design of the refracting telescope (using an objective mirror, instead of a lens), now called the Newtonian telescope.

New and Improved LensesChristian Huygens (1629-1695) was a Dutch physicist and astronomer who developed new methods for grinding and polishing glass telescope lenses (about 1654). With his new, powerful telescopes, he identified Saturn’s rings and discovered Titan, the largest moon of Saturn in 1655. Huygens also invented the pendulum clock in 1656 (eliminating springs), wrote the first work on the calculus of probability (De Ratiociniis in Ludo Aleae, 1655), and proposed the wave theory of light (Traité de la lumiere, 1678).

Reflecting TelescopesJames Gregory (1638-1675), a Scottish mathematician, invented the first reflecting telescope in 1663. He published a description of the reflecting telescope in “Optica Promota,” which was published in 1663. He never actually made the telescope, which was to have used a parabolic and an ellipsoidal mirror.

Cassegrain TelescopeA Cassegrain telescope is a wide-angle reflecting telescope with a concave mirror that receives light and focuses an image. A second mirror reflects the light through a gap in the primary mirror, allowing the eyepiece or camera to be mounted at the back end of the tube. The Cassegrain reflecting telescope was developed in 1672 by the French sculptor Sieur Guillaume Cassegrain. A correcting plate (a lens) was added in 1930 by the Estonian astronomer and lens-maker Bernard Schmidt (1879-1935), creating the Schmidt-Cassegrain telescope which minimized the spherical aberration of the Cassegrain telescope.

Schmidt-Cassegrain TelescopeA Schmidt-Cassegrain telescope (SCT) is a wide-angle reflecting telescope with a correcting lens that minimizes spherical aberration and a concave mirror that receives light and focuses an image. A second mirror reflects the light through a gap in the primary mirror, allowing the eyepiece or camera to be mounted at the back end of the tube. The Cassegrain telescope (named for the French sculptor Sieur Guillaume Cassegrain) was developed in 1672; the correcting plate (a lens) was added in 1930 by the Estonian astronomer and lens-maker Bernard Schmidt (1879-1935).

Radio TelescopesKarl Gothe Jansky (1905-1949) was an American radio engineer who pioneered and developed radio astronomy. In 1932, he detected the first radio waves from a cosmic source – in the central region of the Milky Way Galaxy. Gote Reber (a ham radio operator) made the first true radio telescope (using a 32-foot diameter parabolic dish to focus the radio waves) after reading of Jansky’s discoveries.

Hubble Space TelescopesThe Hubble Space Telescope (or HST) is a powerful telescope in orbit around the Earth. HST transmits pictures and spectra of objects in space without the interference of the atmosphere (which makes telescopic images from the ground have less detail). It was launched into space in April 1990 and was repaired in December, 1993. It was named for the American astronomer Edwin Hubble.